Individuals move on foot in a variety of ways including walking, running, and ascending or descending stairs or sloped surfaces. Gait may be assessed in terms of a gait cycle, also called a stride. A stride begins when a reference foot (either the left or right) makes contact with the ground and ends when it next contacts the ground. A stride is composed of two steps. A step is the action occurring in the interval from the moment that one foot contacts the ground to the moment when the other foot contacts the ground. A step may be attributed to either the left foot or the right foot, though actions of both feet are necessary to take a step.
Gait analysis has been used not only to document gait abnormalities but also to determine the underlying causes of the abnormalities and, in some cases, to select treatment. Instruments used in conventional gait analysis laboratories detect a variety of measures associated with walking. Some measure the position of the body and limbs while others measure the forces resulting from walking or muscle activation involved in walking. However, these conventional gait analysis instruments may be expensive and cumbersome and may only measure a subject's gait in the laboratory and not during activities of daily living.
Over the past decade, accelerometers have become smaller, less expensive, more accurate, and more energy efficient. An accelerometer may refer to a device that measures either linear or angular acceleration. However, accelerometers measuring angular acceleration may also be referred to as gyroscopes, gyrometers, or simply gyros. An accelerometer may also refer to a device that measures acceleration in more than one direction. Three-axis (triaxial) accelerometers in which the axes are at least approximately orthogonal to one another are now a common feature in devices ranging from smartphones to fitness trackers.
Fitness trackers may estimate quantities of physical activity such as step count, calories burned, or distance traveled. However, such quantitative measures provide little information about gait quality. Viewing acceleration data as a signal (in which the x-axis represents time and the y-axis represents the quantity of acceleration) may provide some insight as to gait quality. For signal graphs however, viewers may find it difficult to compare the acceleration data from one step to that of another. Comparing steps in a signal graph requires the viewer to determine boundaries between steps and mentally superimpose the acceleration signal of one step over that of another. Such divisions and superimpositions are mentally taxing. Viewing acceleration signals from multiple axes further compounds the effort required to compare one step to another.
FIG. 1 presents a graph (100) showing three signals representing acceleration along three orthogonal axes of a triaxial accelerometer coupled to an individual taking steps. The graph's horizontal axis (110) represents time in seconds and the graph's vertical axis (120) represents acceleration in g (freefall acceleration in Earth's gravity). Acceleration along the accelerometer's x axis is represented by the bottommost line (130) of the graph (100). Acceleration along the accelerometer's y axis is represented by the topmost line (140) of the graph (100). Acceleration along the accelerometer's z axis is represented by line 150 on the graph (100) which, generally, lies between the other two lines.
Additive manufacturing (also called “three dimensional printing” or “3D printing”) encompasses a variety of techniques used to manufacture objects in three-dimensions using automated, computer-controlled processes. In some types of additive manufacturing, a three dimensional printer (also referred to as an additive manufacturing device) deposits a series of layers. Each layer has a specified shape composed of small, point-like deposits, each of which is placed on a plane according to two coordinates. The deposits forming each layer adhere to the deposits of the layer below it. The number of layers and/or height of each layer effectively act as a third coordinate allowing for the placement of the point-like deposits at precise positions in space. Additive manufacturing may be used to fabricate objects from a variety of materials.